Caldera chronicles: The underloved tuffs of Yellowstone

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Jess Condon, Research Experiences for Undergraduates student, and Madison Myers, assistant professor of Igneous Processes, both at Montana State University.

Over the past 2.1 million years, there have been three very large explosive eruptions from the Yellowstone volcanic system that formed calderas — the Huckleberry Ridge eruption 2.1 million years ago, the Henrys Fork eruption 1.3 million years ago, and the Yellowstone eruption 631,000 years ago.

These eruptions each left a thick deposit of ash called an ignimbrite, which also contains crystals and gas. When the ash, gas and crystals were emplaced, the deposit was so hot that it “welded” into incredibly dense and hard rock. These ash deposits are also known as tuff.

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The tuffs from the Huckleberry Ridge, Henrys Fork and Yellowstone eruptions are well known and get a lot of attention; however, Yellowstone hosts a few more tuffs that, while smaller in volume, are still noteworthy.

Throughout Yellowstone’s history there have been many ‘smaller’ volcanic eruptions (if one considers an eruption 50 times the size of

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